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refcnt_ptr< T > Class Template Reference

#include <refcnt_ptr.h>

List of all members.


Detailed Description

template<typename T>
class refcnt_ptr< T >

refcnt_ptr implements a reference-counting smart pointer class.

In general, refcnt_ptrs do the Right Thing. You can use them as though they were pointers, copy them, assign them, whatever, and the object they point to will continue to live as long as there is at least one refcnt_ptr pointing at it. There are some caveats, some obvious some less obvious. They are:

1. Don't create multiple refcnt_ptr objects from the same raw pointer. Each one of them will delete it. The best usage is to put the raw pointer into a refcnt_ptr as soon as you get it, and then make copies of the refcnt_ptr as needed.

2. Don't create auto_ptrs from refcnt_ptrs, or do other things that might cause the object to be deleted. Yes, this is obvious, but it's worth hammering home anyway: The *only* safe way to delete an object once you've pointed a refcnt_ptr at it is to destroy all of the relevent refcnt_ptrs. There is no analog to auto_ptr::release(). Be extremely careful with refcnt_ptr::get().

3. Don't share refcnt_ptrs across threads, unless you know what you're doing. If you do it, you will need to synchronize all actions that might update the reference count, but be careful because C++ sometimes creates temporary copies where you might not expect, so knowing what needs to be synchronized requires good C++ skillz. Oh, and you obviously need to synchronize uses of the referenced object as well

4. refcnt_ptr supports copying and assignment across compatible types. That is, if T1* is convertible to T2*, then you can copy or assign a refcnt_ptr<T1> to a refcnt_ptr<T2>. This is very convenient, particularly in cases where T2 is const T1, or where T1 is derived from T2. Be careful, however about pointer upcasts to types that don't have a virtual destructor. If you create a Derived and make a refcnt_ptr<Base> point to it, it will get destroyed as a Base, not as a Derived, unless Base has a virtual dtor. IOW, don't slice pointers.

5. Keep in mind that reference counting does have run-time overhead, and it can get to be significant if you use refcnt_ptr mindlessly, because every copy, assignment and destruction of a refcnt_ptr involves updating the reference count -- just a dereference plus an increment or decrement but there are cases where it matters. Space overhead may also be an issue if you have lots and lots of pointers. n pointers to T consume

(n * sizeof(T*)) bytes,

whereas n refcnt_ptr<T>s consume

(n * sizeof(T*) + n * sizeof(int*) + sizeof(int)) bytes.

Plus some structure padding, maybe, depending on the platform. In general, just assume that a refcnt_ptr uses three times as much space as a regular pointer.

Definition at line 84 of file refcnt_ptr.h.


Public Member Functions

int count () const throw ()
T * get () const throw ()
 operator bool ()
T & operator* () const throw ()
T * operator-> () const throw ()
template<typename T2>
refcnt_ptroperator= (std::auto_ptr< T2 > rhs)
template<typename T2>
refcnt_ptroperator= (const refcnt_ptr< T2 > rhs)
refcnt_ptroperator= (const refcnt_ptr &rhs)
template<typename T2>
 refcnt_ptr (std::auto_ptr< T2 > &rhs) throw ()
template<typename T2>
 refcnt_ptr (const refcnt_ptr< T2 > &rhs) throw ()
 refcnt_ptr (const refcnt_ptr< T > &rhs) throw ()
 refcnt_ptr (T *obj=0) throw ()

Private Member Functions

void increaseCount ()
void reduceCount ()

Private Attributes

T * object
int * refCnt

The documentation for this class was generated from the following file:

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